This longitudinal investigation will examine developmental precursors and outcomes of engaging in and being the victim of social and physical aggression. Whereas physical aggression inflicts or threatens bodily harm, social aggression hurts others by damaging their friendships, peer relations, or social status. Social aggression includes behaviors such as social exclusion, friendship manipulation, malicious gossip, and non-verbal efforts at alienation and manipulation. Preliminary studies have established that social aggression hurts children and is related to psychosocial maladjustment, but longitudinal research is needed to explore precursors, stability, and sequelae of perpetrating and being victimized by social and physical aggression. This study will follow a normal sample of 300 children from ages 9 - 14, a developmental period in which social aggression has been shown to become more frequent and intense. This investigation will examine how frequently children engage in and experience these behaviors and explore whether and when gender differences emerge, using multiple methods to measure social aggression (observations and telephone interviews, as well as peer nominations and teacher and parent reports). This study will explore factors that may contribute to individual differences in engaging in and being victimized by social and physical aggression: family, peer group, and school factors. This research will investigate developmental outcomes associated with engaging in and being the victim of social and physical aggression: qualities of peer and romantic relationships, self-concept, academic progress, identity formation, externalizing symptoms, internalizing symptoms, personality difficulties, and eating disorder symptoms. This study will explore developmental precursors of adolescent psychopathology for both girls and boys, with the long-term goal of determining whether reducing social aggression might be helpful in preventing externalizing symptoms, internalizing problems, personality disorders, and eating disorders.